X-ray device



1 w. D. COOLIDGE 1,971,312

X-RAY DEVICE Filed Jan. 16, 1929 Inventor: I William D.Coolid e,

WwZZw His Attorney Patented Aug. 28, 1934 X-RAY DEVICE William n. Coolidge, Schenectady, N. Y. assignor 'to 'Gencral Electric Company,

New York a corporation of Application January 16, 1929, Serial No. 332,918

Claims.

The present invention comprises an improved thermionic X-ray tube wherebya more uniform X-ray emission maybe secured than has been possible heretofore.

Thermionic X-ray tubes have been provided heretofore with filamentary cathodes, which usually have assumed the form of helices or spirals. The electrons projected from such a filamentary cathode upon the target strike the target on lines .10 substantially corresponding to the linear form of the cathode, hence producing a non-uniform dis tribution of X-rays in the emitted beam. Furthermore, the intense electrostatic field existing in an X-ray device due to the high voltages imi pressed on the electrodes will cause distortion or damage to a filamentary cathode, unless a construction is used whereby the cathode is shielded or otherwise protected.

In accordance with the present invention, I

have provided an X-ray device having a cathode which is constructed to provide a broad area (as contrasted with a filament) which is capable of being operated at a uniform temperature and,

hence being capable of emitting an electron beam m5 of uniform cross-sectional intensity. The cathode structure embodying my invention includes also a focusing device and means for heating the cathode to a temperature at which effective electron emission occurs.

7-30 My invention is illustrated in the accompanying $235 and Fig. 4 is a diagram of electrical connections.

The X-ray device comprises the usual sealed and evacuated envelope 1 in which are located an anode 2 and a cathode 3. The anode (sometimes known as target or anti-cathode) ordi- 40 narily consists of a refractory metal, for example, tungsten. The structure for supporting the stem 4 of the anode has been diagrammatically indicated at 5.

As shown in Fig. 2 the cathode structure, taken as a whole, comprises a plate or disc 3 having any desired shape. This plate is supported by a relatively slender stem 6. The plate has sufiicient thickness to be capable of operation at a substantially uniform temperature in spite of slight losses @330 of heat through the stem 6 which as later explained is itself independently heated and hence not a channel for substantial heat loss. Surrounding the cathode plate 3 is a focusing device 7 constituted by a flanged cylinder which is supported by wires 8, 9, and which may consist of nickel, molybdenum or other suitable metal. The rim or mouth of the focusing cylinder 37 isclosely adjacentjtobutpreferably doesnot touch disc 3, so as to avoid heat losses and, reduction oftemperature atthe edge. of the heatedcathode.

Closely adjacent to and on the rear of the cathode plate 3 is a spiral filament l0 whichis connected to conductors 11, 12 whereby heating energy may be supplied. The stem 6 and the various conductors are all bound together by an insulating clamping plate 13 whereby the conductors are held in spaced relation. A supporting device 14 of the usual construction is indicated in Fig. 1.

As clearly shown in Fig. t the filamentary electrode 1G is connected to a source of current 15 (represented as a battery) in series with a regulator 16 (represented as a resistance) for a supply of heating energy. The source 1'7 (also shown as a battery) in series with a regulator 18 produces a thermionic discharge between the filament l0 acting as cathode and the plate 3 acting as anode, thereby causing the plate 3 to be heated to a temperature of electron emission. It can then serve as cathode with respect to the anode or target 2 to produce X-rays, energy being supplied by the secondary of the transformer through the conductors 29, 21. The stem 6 also receives energy by bombardment of electrons from the auxiliary cathode 10, and hence withdraws substantially no heat from the plate 3.

A beam of X-rays emitted by my improved device has an essentially uniform distribution over a section normal to the axis of the beam. Furthermore, the described construction permits of 91 locating the cathode more closely to the anode than practicable with a filamentary cathode.

In the modified cathode structure shown in Fig. 3 cathode disk 3 is suppcrted at its circumference by the focusing cylinder 7, as by tabs 23 which join the outer rim of the plate 3 and the inner rim of the focusing cylinder at three points so as to maintain a poor heat conducting relation between the cathode and the focusing member and thereby to permit of operating the cathode at a substantially uniform electron emission temperature.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In an electric discharge device, a cathode structure comprising a plate, heating means located adjacent said plate, a support for said plate, a plurality of tabs positioned about the plate for spacing the latter from said support whereby the 3. An X-ray device comprising an envelope, a

target, a plate-shaped cooperating cathode, a support for said cathode, said support including a focusing member secured to the cathode but in poor heat-conducting relation therewith, and means for heating said cathode, the cathode being constructed and supported to operate at a substantially uniform electron emission tempera-- ture.

a. An X-ray device comprising an envelope, cooperating main electrodes in said envelope, one of said electrodes comprising a plate of refractory metal, means for heating said plate to an electronemitting temperature, a combined means for supporting said plate and for focusing the electrons onto the other of said main electrodes, said combined means including a member surrounding said plate and secured at its inner edge to said plate but in poor heat-conducting relation therewith whereby heat is substantially prevented from leaving the plate at the places Where it is secured to the focusing member and whereby said plate is maintained at a substantially uniform temperature over the entire surface.

5. An X-ray device comprising an envelope, cooperating electrodes therein, one of said elec trodes comprising a plate of refractory metal, a heater for said plate, means for supporting the plate Within the envelope, said means including a cylindrical member surrounding the plate and secured at its inner edge to said plate but in poor heat-conducting relation therewith whereby heat is substantially prevented from leaving the plate at the places where it is secured to said member and whereby said plate is maintained at a substantially uniform temperature over its entire surface.

WILLIAM D. COOLIDGE. 

